There is abundant and increasing laboratory and clinical evidence that moderate levels (42.0- 44.5 degrees C) of sustained local hyperthermia can regularly effect a delay in the growth of certain types of malignant tumors, often a complete regression, and even a permanent control. Currently for production of controllable levels of local hyperthermia restricted to the target volume of tissue irrespective of its anatomical location, insonation with a focused beam of continuous wave low megahertz ultrasound is the modality of choice. Extensive studies have established the fact that the effects of such insonation on organized mammalian tissues are predominantly thermal in nature, the magnitude of non-thermal effects, e.g. cavitation, which might induce metastatization, is negligible except at very high intensity levels. A scaled-down laboratory prototype of a computer-controlled insonation system, for deposition of ultrasonic energy throughout a predetermined volume of tissue (10 cm X 10 cm X 10 cm on full scale) by scanning the region in a programmed manner, has been demonstrated to produce and maintain the prescribed level of hyperthermia uniformly throughout the target volume for the desired duration. No evidence of tissue damage has been observed histologically even with isonation induced hyperthermia, sustained for periods of up to six hours. Design and fabrication of a full-scale clinical model and its tests in large animals are proposed. Grey scale - B scan ultrasonic imaging techniques are well established in the diagnosis of soft tissue tumors and in radiation therapy planning. Being relatively inexpensive compared to X-ray scanners, such an ulrasonic scanner will be used for providing tumor position information to the computer. Focused ultrasound is also a well proven and unique tool for trackless, focal surgery of deep structures. The proposed clinical system will permit its use for non-invasive surgery of tumors in the "Search and Destroy" mode simply by raising the ultrasonic frequency and intensity.